The present invention relates generally to detectors which detect charged subatomic particles, and more specifically to a diagnostic device which allows direct viewing of Cerenkov radiation beam dynamics at subnanoseconds time-scales.
The experimental study of intense relativistic electron beam dynamics at subnanosecond time-scales is a subject of considerable interest. In this range, electromagnetic waves travel over distances of a few centimeters and collective behavior cyclotron effect and instability growth can be resolved in many important instances.
Among the numerous diagnostics designed for such studies, those allowing a direct viewing of the beam dynamics are of special interest: they offer a simple and accurate description of particle motion and permit fast interactive scanning of the experiment parameters. Unfortunately, intense relativistic electron beams are prone to various instabilities with growth times of tens to hundreds of picoseconds. Even if the electron beam is macroscopically stable, the beam quality, namely, the emittance and brightness, may well be strongly time dependent. Such is the case of electron beams produced by guns with field emission cathodes, photoelectric cathodes, and laser driven field emission cathodes. The task of detecting and observing Cerenkov radiation is alleviated to some extent, by the systems disclosed in the following U.S. Patents, the disclosures of which are incorporated by reference: U.S. Pat. No. 3,049,619 issued to F. Genovese; U.S. Pat. No. 4,429,228 issued to D. Anderson; U.S. Pat. No. 4,389,568 issued to E. Dowdy et al; and U.S. Pat. No. 4,497,769 issued to N. Nicholson et al.
U.S. Pat. No. 4,497,769 discloses a portable instrument for measuring induced Cernekov radiation associated with irradiated nuclear fuel assemblies. U.S Pat. No. 3,040,619 discloses a differential Cerenkov counter for detecting and counting charged subatomic particles. U.S. Pat. No. 4,429,228 discloses a photoionization detector which is an x-ray imaging device.
U.S. Pat. No. 4,389,568 discloses a method for monitoring irradiated fuel inventories located in a water-filled storage pond. In this system, by E. Dowdy et al, the intensity of the Cerenkov radiation emitted from the water in the vicinity of the nuclear fuel is measured.
The above-cited references are exemplary in the art of detecting Cerenkov radiation. Particularly of note is the Nicholson et al reference, which discloses a photometric imaging system which measures induced Cerenkov radiation associated with irradiated nuclear fuel assembles.
Unfortunately, most of the imaging techniques available to date do not give both good space and time resolution. One obtains either spatially resolved, time-integrated pictures (cameras, fluorescent screens etc.), or space integrated, real time measurements (photomultipliers tubes, pin photodiodes, image intensifiers, etc.). More sophisticated diagnostics, such as the magnetooptic shutter, reduce the integration times down to the microsecond range with a good spatial resolution, and optical gates of a few tens of nanoseconds can be obtained with a microchannel plate, but in many instances these time scales are still much longer than those characteristics of the beam dynamics. The streak camera is a very fast diagnostic (typical streak velocity of the order of 1 mm/ns) able to resolve subnanosecond events; its main drawback being that it basically works as a one-dimensional imaging device since one axis of the picture is lost to the streak process.
In view of the foregoing discussion, it is apparent that there currently exist the need for a Cerenkov electrooptic detection system which allows direct viewing of Cerenkov radiation beam dynamics at subnanosecond time-scales. The present invention is intended to satisfy that need.